Class A Watts

I disagree.

"The why of it is that all amps, tube or transistor (or class D) make more distortion into 4 ohms as opposed to 8 or 16 ohms. This distortion is audible as increased brightness and loss of detail. Put in a nutshell, if **Sound Quality** is your goal, it is best served by a speaker of 8 ohms or more."

OK, I'm following the theory, but as far as audible distortion, wouldn't this be more evident with a tube amp (let's say a SET amp) using a 4 ohm spkr rather than a SS amp into a 4 ohm speaker.
Wouldn't this distortion with SS amps show up more on test specs, not in a listening room?

I think so.

Ralph (Atmasphere), Class A, AB, etc aside, I think it's also worth mentioning that many tube amps use negative feedback which reduces the output impedance at the taps. I would surmise that if a tube amp's output impedance off the 8 ohm tap is 1 ohm, and say half that off the 4 ohm tap, the tube amp may behave somewhat "SS-like" in the way it drives speakers that were voiced to be driven by a SS amp.

For example, I understand that the output regulation of my amp is approx. 1.2 db off the 8 ohm tap, which I think permits the inference that my amp can drive a speaker with a varying impedance plot so that the speaker's output SPL as a function of FR is pretty flat. Perhaps even better performance off the 4 ohm tap. Of course, there's the issues you have written so much about: odd ordered harmonic distortion and TIM distortion.

I think this post summarizes the numerous on-line and off-line conversation I have had with you and Al.

Regards,

Bruce

Lowrider57, the way the two types of amplifier technologies distort is somewhat different.

With tube amps you might get a bit more of the lower orders (so you would get a richer, fatter sound, that could border on muddy, as those are all terms audiophiles use to describe excessive lower-ordered harmonic distortion), but this is highly dependent on the actual amp design and its output transformer (if it has one).

With SS amps, there seems to be less variation in the distortion types that creep in- it appears to be almost entirely odd orders (the source of brightness/harshness in many amps). It may not be much but because the human ear/brain system uses odd ordered harmonics to sort out how loud a sound is, it is very sensitive to these harmonics.

***IOW, it shows up in the specs and is also audible.***

As an additional note, 4 ohm speakers are very critical of speaker cables so if you want the best results with them the cable can't be skimped. Conversely with 16 ohms the cable is hardly critical at all- so you can run longer lengths of lighter gauge and totally get away with it.

The reason for this is the seemingly very slight DC resistance of the cable is in series with the output impedance of the amplifier, and can affect the damping factor by quite a lot! BTW this particular fact has been known for decades; I first saw it in a nomograph published by RCA in the early 1960s.

Four ohms came in as a means of allowing speaker manufacturers to seem to not loose so much efficiency while at the same time using cheaper drivers that have less precision in the voice coil gaps and the like (this makes the speaker easier/cheaper to build, as much as 10X cheaper, so its a pretty powerful incentive). You get 3 db of Sensitivity back if you have a transistor amp that can double power. The trick is understanding the Sensitivity and Efficiency are not the same thing!!

This is why I say that 4 ohms offers a *sound pressure* advantage, not a sonic advantage.

You can talk to any amplifier manufacturer and they will tell you the same thing- that fact that their amp can double power into 4 ohms is not the same thing as saying that the amp is sounding its best into that impedance.